The present invention relates to methods and catalysts for the removal of chemically combined sulfur and nitrogen from carbonaceous liquids. Various carbonaceous liquids are contemplated such as those produced in the liquefaction of coal, oil shale, tar sands, etc.
Of particular interest are those carbonaceous liquids produced in the solvent refining of coal. One process for refining coal in this manner is operated by the Pittsburg and Midway Coal Mining Co. in Fort Lewis, Washington. In this process pulverized coal is mixed with recycled solvent or slurry, preheated and held in a dissolver in the presence of hydrogen gas, and further processed to produce fractions of synthetic natural gas, liquid petroleum gas, light distillate, fuel oil and inert ash. The light distillate is often identified as naphtha while the fuel oil fraction comprises middle and heavy distillate.
Unfortunately each of these liquid products, particularly the heavy distillate, include excessive amounts of chemically combined nitrogen and sulfur that make them unsuitable for use as boiler fuels and other applications. Typical levels by weight of 0.5-1.5% combined nitrogen and 0.2-0.8% combined sulfur are found. For boiler furnace fuels, these heavy fractions should be reduced to less than 0.5% nitrogen and 0.5% sulfur by weight. However, if the product is to be employed as a feedstock for a catalytic cracker, the nitrogen requirements are more stringent and are typically required in the range of 100-400 ppm to avoid poisoning hydrocracking catalysts. However a few hydrocracking units tolerate feedstock with nitrogen levels as high as 0.3 but no more than 0.4 weight percent. Previous catalytic materials for hydrotreating solvent refined coal liquids have proven inadequate in consistently denitrogenating to these low concentrations.